1) Field of The Invention
The invention relates to electric lamps and, more particularly, to the manufacture and assembly of lamp bases onto lamp envelopes.
2) Description of the Prior Art
Electric lamps typically have lamp bases or caps Which are manufactured separately from the lamp and are secured to the lamp envelope after sealing of the envelope in a gas-tight manner. The bases are secured to the lamp envelope using a basing cement and/or by a mechanical locking between the lamp cap and the lamp envelope. The separate manufacture and fixation of lamp bases to lamp envelopes inevitably results in breakage and/or loss of bases and the resulting costs associated therewith.
Examples of lamps having cemented bases include General Lighting Service (GLS) incandescent lamps having Edison screw bases, and S-8 type automotive lamps having bayonet bases. In these lamps, the base is fixed to the lamp envelope using a phenolic resin cement. A disadvantage of using cement is that special handling is often required for the cement, for example, to control its temperature and moisture content, and the cement must be cured during lamp manufacture, all of which may add significantly to lamp processing time and cost. For some cements, the curing time may be lessened by the application of heat, but this also adds to the expense of the lamp.
In addition to the processing disadvantages, the bonding between the lamp cap and the envelope has often been found to be less than satisfactory. Some basing cements are adversely effected by high humidity during curing and in storage or service. Moisture absorbed into the cement may reduce the strength of the cement bond and the effectiveness of the seal between the lamp cap and the lamp envelope. The weakened bond poses a hazard to users of the lamp because upon attempted removal of the lamp from its socket, the lamp bulb may separated from the cap, possibly breaking the bulb, and leaving the cap in the socket rendering its removal difficult, if not hazardous. Additionally, for lamps exposed to the environment, such as S-8 automotive lamps having a brass bayonet base, the cement provides an ineffective seal, allowing moisture, dust, and dirt to infiltrate between the brass base and the envelope, causing corrosion of the lead-wires and the base.
Lamps having mechanically secured lamp bases typically have discontinuities such as ridges or channels in the neck, stem, or pinch seal area, lockingly engaged by corresponding discontinuities on the lamp cap. For example, U.S. Pat. No. 4,849,670 and U.S. Pat. No. 4,146,814 show a one and two-piece metallic lamp cap for a single-ended miniature incandescent lamp having tangs or corrugated projections which extend in axial grooves in the pinch seal. Generally, to ensure correct positioning and a strong fixation, the dimensions of the mating parts of the lamp envelope and base must be tightly controlled. Additionally, multi-piece lamp caps of synthetic material are known which snap together and lock on the lamp envelope. In addition to possible integrity problems with the extra connection between the parts, this type of base adds to the number of parts which must assembled.
In recent years, the use of lamp bases or caps of synthetic material, especially in automotive lamps, has become more common. Such lamp caps typically have pin or tongue-shaped contacts fixed therein or use the lamp lead-throughs as contacts. Lamp caps of synthetic material are generally manufactured by injection molding and are later fixed to the lamp envelope either by cement or by mechanical fixation, and suffer from the same lamp manufacturing disadvantages as discussed above with respect to metallic bases. For example, U.S. Pat. No. 4,864,185 shows an S-8 type automotive lamp having a lamp cap of synthetic material which is secured to the lamp envelope by an epoxy cement.
Despite the use of synthetic material for the lamp cap, protection of the lamp lead-ins from moisture and dirt remains a problem in many lamps. In U.S. Pat. No. 4,687,965, a type 9005/9006 automotive head lamp having a lamp cap of synthetic material is shown. The lead-ins pass through aperture in an end wall of a dish-shaped part and are welded to the ends of tongue-shaped contact terminals. A synthetic foam material or RTV silicone rubber is required in these lamps to protect the welded connection between the terminals and the lead, and to prevent moisture and dirt from infiltrating through the apertures in the end wall. In the above mentioned U.S. Pat. No. 4,864,185 the leads are passed through channels in the lamp cap through which moisture, dust, and dirt may infiltrate if an effective seal is not maintained between the lamp cap and its socket.
Other lamps having bases of synthetic material include compact low pressure mercury vapor discharge lamps in which the adjacent ends of an elongate discharge tube are supported in a mounting plate or base member of a lamp bowl or shell. For example, U.S. Pat. No. 4,853,583 shows a PL* type compact fluorescent lamp having the adjacent ends of the discharge tube fixed by cement in a metallic base portion which is secured to a lamp shell, holding the starter, by rivets. U.S. Pat. Nos. 4,375,607 and 4,503,360 show SL* type compact fluorescent lamps having a bowl-shaped shell in which the adjacent ends of the discharge tube are secured in a mounting plate or base member of the shell by cement.
Accordingly, it is an object of the invention to provide an electric lamp having improved fixation of the lamp base, or base portion, to the lamp envelope.
Another object of the invention is to provide a lamp having a base with a cementless connection to the lamp envelope.
Another object of the invention is to provide an electric lamp having a lamp base which can be provided on the lamp envelope at reduced cost to bases known in the art.
Yet another object of the invention is to provide an electric lamp having a lamp base which can be formed directly on the lamp envelope.
Still another object of the invention to provide an electric lamp having improved sealing of the lamp base to the envelope and protection of the lamp leads.